The present invention relates primarily to a method and system for producing an output corresponding to a safety level, particularly in relation to an activity on a moving body. One embodiment of the present invention relates to a method and system for producing an output indicative of a safety level for a vessel at sea, such that a user may assess the data produced to determine if a task can be performed within a safe working limit.
Personnel responsible for the safety and security of aircraft aboard warships have for many years relied on roll and pitch limits to form the basis of information to determine if tasks can be performed within a safe operational window. It is known that these limits are in some cases over restrictive, as in times of emergency they have been exceeded without incident.
Attempts to expand the operational window by providing alternative and more detailed information in the form of data relating to the heading of the vessel to the waves (also termed wave encounter angle), along with that of roll and pitch limits, or by providing data based on speed-polar plots and sea state have, in the main, proved unsuccessful, because users have been unable to readily and objectively interpret the data supplied to them.
In particular, speed-plots suffer front a number of limitations, the greatest of which is the subjective determination of sea state, based on an estimation of wave height and direction. Other variables can also affect the validity of the speed-plot: the models used in the ship motion program to generate speed-plots are formulated from idealistic models, and do not account for changes in, for example, the ship mass, centre of gravity, trim, and stabiliser response.